absorption or diffusion for small room?

[tonyton]

i just want to treat a bit more my live room, dimentions are 17ft L, 11W, 10H. so far i have covered almost all corners of the room with bass traps and broadband absorbers, including the corners between the walls and ceiling, also there are some broadband absorbers on some walls. One of the walls though is not covered with anything...its painted concrete, 11ft W and 10ft H... so i m wondering if its worth buylding a large QRD diffusor for that wall or just adding more absorption....will the diffusor make a room like this sound "bigger"? the room is quite dead already...so i m not sure what to do, i would appreciate any help, thanks

[Ethan Winer]

Your room is definitely large enough to benefit from diffusion on the rear wall behind you. And Yes, that will make the room sound larger.

--Ethan

[wshaw]

What about putting diffusion on the ceiling?

I have a smilarly-sized room, about 12 x 15 ft. with 9.5 foot ceiling. It's quite crowded with gear, drums, bookcases, and bass trapping, so there's no place for any diffusion except on the ceiling.

I'm thinking of running a strip of diffusion on the ceiling near the rear wall. Like 3 T-fusors, in a line, with the panels pointing in different directions, for a total 6feet wide by 2 feet front-to-back.

Think it'll do much good, or am I better of putting absorption up there? I should mention that the floor has pretty dense carpet, the walls have boocases and a fair amount of acoustic panels, and the ceiling already has three 2 x 4 foot 2-inch panels.

[SAC]

I would employ just enough absorption on the ceiling to eliminate early hot reflections in the Initial Signal Delay gap period and employ 1D diffusion (such as QRD/PRDs - or even polys in a pinch) on the back and rear side walls as Ethan has suggested.

You are in very close proximity (relatively speaking) to the ceiling sources and the lack of spatial control with T-Fussors is not going to help with a creation of an effective initial signal delay (ISD) period (if you are attempting to do this).

Thus, due to the close proximity and the lack of effective pattern control, you will be redirecting energy back into the ISD, which is not advantageous.

If you are not going to be absorbing the ceiling energy, sound from above lacks substantial psycho-acoustic merit and as such the energy is better redirected from the ceiling to the rear and rear-side surfaces where it can be diffused and then reintroduced laterally (rear-side) to the listening area after the ISD period is terminated.

This laterally arriving diffuse energy is optimal to terminate the ISD region with returns that are a Maximum of 10-12 dB (SPL) down from the direct signal level. Achieving this gain level is no trivial feat in a small room using lots of bass trapping unless the bass traps are very frequency selective.

Diffusion is optimal when it arrives from the rear lateral surfaces. (in other words, the rear-sides). Thus 1D diffusion on the wallrear and rear side walls redirecting the sound in the horizontal plane is more advantageous than using 2D diffusion and redistributing energy to the ceilings and flows where it is harder to make use of it productively.

[Jens Eklund]

You can try this if the room is small (making it somewhat tricky applying diffusers sometimes):

11m2 control room? Placement of acoustic elements


Sincerely Jens Eklund

[wshaw]

Wonderful information--thank you!

So, I gather that the concern is this: if the diffusion element is too close to the listening position, scattered energy will reach the listening position in sufficient quantities to create new issues.

In the setup I'm describing, the diffusion elements wouild be 5 to 7 feet behind the listening position, and about 5 feet above the listening position, or about 7 linear feet away.

Hmmm--to my untrained eyes, that seems pretty darn close. It makes sense that some diffused energy from the ceiling would make it back to my ears.

OK. Let's scrap that idea.

Many thanks!!!!

[Jens Eklund]

Originally Posted by wshaw

Wonderful information--thank you!

So, I gather that the concern is this: if the diffusion element is too close to the listening position, scattered energy will reach the listening position in sufficient quantities to create new issues.

In the setup I'm describing, the diffusion elements wouild be 5 to 7 feet behind the listening position, and about 5 feet above the listening position, or about 7 linear feet away.

Hmmm--to my untrained eyes, that seems pretty darn close. It makes sense that some diffused energy from the ceiling would make it back to my ears.

OK. Let's scrap that idea.

Many thanks!!!!

Usually the ISD determines the placement of diffusers. If scattered energy falls within the IDS, I would choose another treatment (or perhaps angle a 1D diffuser so the energy is scattered away from the sweet spot).

/Jens

[wshaw]

Angling the diffusor is an interesting idea. However, I doubt that it would pass the spouse approval test. . . . tutt

[wshaw]

How about this--

I own ten snare drums. If I put them on a shelf on the rear wall they'd present a somewhat broken-up hemisperical surface for a length of over 6 feet.

Would that make for useful diffusion in my 12 x 15 x 9 foot room?

[SAC]

First of all their surface area is small.

Secondly, you are proposing using objects that will very most likely audibly resonate as a source of scattering...
If this is the case, use polys instead.

And thirdly, and perhaps most importantly, do you have measurements that show what is actually happening in the room, and have you chosen an acoustical response model that will determine what treatment is appropriate to create a desired final result - or are you simply adding diffusion because others have mentioned it and it seems like something to be added as an afterthought as well? Sorry, but without a coherent plan, that is exactly what it is.

[wshaw]

I put muffling on the drums and in between the snare head and snare wires, so there isn't much resonance.

Each drum is indeed a small surface. From looking at commercial diffusers, though, they look like a lot of broken-up surfaces, and that's what the drums present, sort of.

What if I put some of them vertical and some of them horizontal, to increase the size of the spray of scattered energy?

[Glenn Kuras]

I think I would sell the snare drums and get some real diffusion.

[Jens Eklund]

Originally Posted by Glenn Kuras

I think I would sell the snare drums and get some real diffusion.

+1

[wshaw]

Yeah, well, kinda, like . . . I dunno about that . . . I kinda likes my snares . . .

Any other ideas?

[Weasel9992]

Originally Posted by wshaw

I own ten snare drums.

Drummers and snare drums...it's like guitar players and guitars.

[wshaw]

For Gadd's sakes, folks, me without my snare arsenal . . . YIKES . . . :

[Torea]

Originally Posted by Weasel9992

Drummers and snare drums...it's like guitar players and guitars.

Or Engineers and mics/pres/outboard/plugins... haha